The invention relates to a steel tube butt welding machine which comprises a machine frame, wherein a main shaft driven by a driving device to rotate intermittently and arranged vertically is connected to the machine frame in a rotary mode, a rotary disc is mounted on the top of the main shaft, at least three rotary shafts distributed at intervals in a circular mode are connected to the rotary disc in a rotary mode, driving motors driving the rotary shafts to rotate respectively are further mounted on the rotary disc, and a lower steel tube clamp is mounted on the top of each rotary shaft; supporting frames arranged corresponding to the rotary shafts respectively are further mounted on the rotary disc, an upper positioning air cylinder is mounted on each supporting frame, and an upper steel tube clamp is mounted on a downward extending piston rod of each upper positioning air cylinder; a welding machine body and a welding gun fixing base are further mounted on the machine frame, a welding gun of the welding machine body is connected to the welding gun fixing base in a rotary mode and is driven by a driving handle to rotate, and a positioning plate used for positioning the angle of the welding gun is further mounted on the welding gun fixing base. According to the steel tube butt welding machine, product clamping processes are simplified, welding efficiency and quality are improved, the weld appearance quality of a product produced with the welding machine is good, labor intensity of workers is relieved greatly, and product welding time is shortened.